Barrett's esophagus is diagnosed by-

"The definition of Barrett's esophagus (BE), has evolved considerably over the past decade. Traditionally, BE was identified by the presence of columnar mucosa extending at least 3 cm into the esophagus. It is now recognized that the specialized intestinal-type epithelium found in Barrett's mucosa is the only tissue predisposed to malignant degeneration. Consequently, the diagnosis of Barrett's esophagus is presently made given any length of endoscopically identifiable columnar mucosa that proves on biopsy to show intestinal metaplasia. While long segments of columnar mucosa without metaplasia do occur, they are uncommon and are probably congenital in origin. The hallmark of intestinal metaplasia is the presence of intestinal goblet cells." Ref : Schwaz 9/e p831